Titus Livius (Livy), The History of Rome, Book 4
Rev. Canon Roberts, Ed.

17. During¹ their magistracy Fidenae, where a body of Romans were settled, revolted to Lars Tolumnius, king of the Veientines. [2] The revolt was made worse by a crime. C. Fulcinius, Cloelius Tullus, Sp. Antius, and L. Roscius, who were sent as envoys to ascertain the reasons for this change of policy, were murdered by order of Tolumnius. [3] Some try to exculpate the king by alleging that whilst playing at dice he made a lucky throw and used an ambiguous expression which might be taken to be an order for death, and that the Fidenates took it so, and this was the reason of the death of the envoys. [4] This is incredible; it is impossible to believe that when the Fidenates, his new allies, came to consult him as to committing a murder in defiance of the law of nations, he should [5??] not have turned his thoughts from the game, or should afterwards have imputed the crime to a misunderstanding. [6] It is much more probable that he wished the Fidenates to be implicated in such an awful crime in order to make it impossible for them to hope for any reconciliation with Rome. The statues of the murdered envoys were set up in the Rostra.

Owing to the proximity of the Veientines and Fidenates, and still more to the heinous crime with which they began the war, the struggle threatened to be a desperate one. [7] Anxiety for the national safety kept the plebs quiet, and their tribunes raised no difficulties in the election of M. Geganius Macerinus as consul for the third time, and L. Sergius Fidenas, who, I believe, was so called from the war which he afterwards conducted. [8] He was the first who fought a successful action with the king of Veii on this side of the Anio. The victory he gained was by no means a bloodless one; there was more mourning for their countrymen who were lost than joy over the defeat of the enemy. [9] Owing to the critical aspect of affairs, the senate ordered Mamercus Aemilius to be proclaimed Dictator. He chose as his Master of the Horse L. Quinctius Cincinnatus, who had been his colleague in the college of consular tribunes the previous year, a young man worthy of his father. [10] To the force levied by the consuls were added a number of war-seasoned veteran centurions, to fill up the number of those lost in the late battle. The Dictator ordered Quinctius Capitolinus and M. Fabius Vibulanus to accompany him as seconds in command. [11] The higher power of the Dictator, wielded by a man quite equal to it, dislodged the enemy from Roman territory and sent him across the Anio. He occupied the line of hills between Fidenae and the Anio, where he entrenched himself, and did not go down into the plains until the legions of Falerii had come to his support. [12] Then the camp of the Etruscans was formed in front of the walls of Fidenae. The Roman Dictator chose a position not far from them at the junction of the Anio and the Tiber, and extended his lines as far as possible from the one river to the other. The next day he led his men out to battle.